Continuous-Wave Group

LIGO Scientific Collaboration and Virgo Collaboration

Public Web Pages

The LSC-Virgo Continuous-wave ("Pulsar") Working Group searches for continuous-wave
gravitational radiation in data from the LIGO, Virgo, and
GEO 600 gravitational wave detectors. The most likely
sources of such radiation are rotating neutron stars in
our Galaxy. A small bump on the star's surface (~mm high or less) or a slight wobble in its rotation
could generate gravitational disturbances that would be detectable as waves here on Earth.

We carry out searches for
radiation both from known pulsars (neutron stars that regularly beam
electromagnetic radiation toward the Earth) and
from as-yet-undiscovered neutron stars.
In searching for continuous-wave sources, one must make
corrections for the Earth's rotation and orbital motion
around the Sun. These corrections depend on the precise
location of an assumed source and become increasingly
important as the time of observation increases. An all-sky
search for sources spinning at detectable frequencies, if
carried out at the intrinsic sensitivity of the interferometers,
would exhaust the capability of all computers in existence!

As a result, one must make tradeoffs in sensitivity
(or distance at which a source of given luminosity can be seen) in order to cover
a large parameter space (sky location, frequency, frequency spindown).
A variety of search methods have been developed that
make different choices for those tradeoffs in searches
carried out in the first six LIGO science runs (S1-S6) and first
four Virgo science runs (VSR1-VSR4) to date.
More information can be found in the publications linked below.

The most ambitious search we carry out is called Einstein@Home,
one of the world's largest distributed-computing projects, modeled
on and supported by the pioneering Seti@Home project. The Einstein@Home
project allows any interested person to help search for unknown
neutron stars by downloading a program that runs in background
on a personal computer when the computer is otherwise idle.
Einstein@Home has an eye-catching screen saver that shows a
rotating celestial sphere, with the pulsars in the Milky Way marked in color.
Although Einstein@Home has not yet found gravitational waves from a
neutron star, it hasdiscovered a new milli-second radio pulsar
(PSR J2007+2722) in radio data from the Arecibo Observatory.

An especially notable result to date is a limit on the strength of
gravitational radiation emitted by the Crab Pulsar, a young neutron
star (created in a supernova reported by Chinese astronomers in
1045 A.D.) with a radius of only ~10 km, but more massive than the Sun,
and spinning on its axis 30 times per second! The Crab's rotation
frequency is decreasing perceptibly, implying a significant energy
loss. Our most recent limits indicate that no more than one percent of
that energy loss can be attributed to gravitational wave emission.

We are wrapping up searches in the data from the most sensitive of the initial LIGO and Virgo science
runs (LIGO S5-6, Virgo VSR2-4) as we start looking at data from the first Advanced LIGO
Observing run O1 (fall 2015).

Observational results to date

Known neutron stars

Setting
upper limits on the strength of periodic gravitational waves from PSR
J1939+2134 using the first science data from the GEO 600 and LIGO
detectors.

Meetings with Neutron Star Astronomers

We have hosted a series of meetings with neutron star experts since October 2006,
in order to ensure that the tradeoffs we make in our computationally limited searches
are guided by the latest observational results and theoretical findings. These meetings
have proven useful, with the most recent held in Boston
in May 2011. Astronomers with an interest in
gravitational wave emission from neutron stars are strongly encouraged to attend.
Below are the web sites for the meetings in this series.